Performance issue when writing to google docs sheet via apps script - google-apps-script

Question

I use apps script to connect to an SQL database and execute a query. It works as intended but writing the result to a docs sheet takes too long. The execution exceeds the timeout long before all rows are written. The query itself is executed relatively fast (<10s) but writing the lines (over 12000 results) happens very slowly. I use the following code:
var server = 'x.x.x.x';
var port = 3306;
var dbName = 'xxx';
var username = 'xxx';
var password = 'xxx';
var url = 'jdbc:mysql://'+server+':'+port+'/'+dbName;
function readData() {
var conn = Jdbc.getConnection(url, username, password);
var stmt = conn.createStatement();
var results = stmt.executeQuery('insertQueryHere');
var metaData=results.getMetaData();
var numCols = metaData.getColumnCount();
var spreadsheet = SpreadsheetApp.getActive();
var sheet = spreadsheet.getSheetByName('sheet123');
sheet.clearContents();
var arr=[];
for (var col = 0; col < numCols; col++) {
arr.push(metaData.getColumnName(col + 1));
}
sheet.appendRow(arr);
while (results.next()) {
arr=[];
for (var col = 0; col < numCols; col++) {
arr.push(results.getString(col + 1));
}
sheet.appendRow(arr);
}
results.close();
stmt.close();
sheet.autoResizeColumns(1, numCols+1);
}
Any idea on how to improve performance?

Answer 1

You are making repeated calls to the server with appendRow(). Instead collect all the new rows in an array and use setValues(). See Best Practices
function readData() {
var conn = Jdbc.getConnection(url, username, password);
var stmt = conn.createStatement();
var results = stmt.executeQuery('insertQueryHere');
var metaData=results.getMetaData();
var numCols = metaData.getColumnCount();
var spreadsheet = SpreadsheetApp.getActive();
var sheet = spreadsheet.getSheetByName('sheet123');
sheet.clearContents();
var arr=[];
var rows = [];
for (var col = 0; col < numCols; col++) {
arr.push(metaData.getColumnName(col + 1));
}
rows.push(arr);
while (results.next()) {
arr=[];
for (var col = 0; col < numCols; col++) {
arr.push(results.getString(col + 1));
}
rows.push(arr);
}
sheet.getRange(sheet.getLastRow()+1,1,rows.length,numCols).setValues(rows);
SpreadsheetApp.flush(); // just to make sure the data is written
results.close();
stmt.close();
sheet.autoResizeColumns(1, numCols+1);
}